1. Field of the Invention
The present invention relates to a mounting structure of a monolithic capacitor including outer electrodes on an elementary body that includes dielectric layers and inner electrodes, which are alternately stacked, and also relates to a monolithic capacitor mounted in the mounting structure.
2. Description of the Related Art
At present, monolithic capacitors are widely utilized in various electronic devices, including cellular phones and other mobile terminals, personal computers, etc. The monolithic capacitor includes an elementary body having a substantially rectangular parallelepiped shape and functioning as a capacitor. The elementary body has a structure in which dielectric layers and electrodes (inner electrodes), each being in the form of a flat plate, are alternately stacked. That type of monolithic capacitor includes outer electrodes connected to the inner electrodes. The outer electrodes are generally formed at both ends of the elementary body in the lengthwise direction thereof, respectively.
The above-described monolithic capacitor is electrically and physically connected to a circuit board of an electronic device by directly placing the outer electrodes on mounting lands of the circuit board, and by bonding the mounting lands and the outer electrodes to each other using a bonding material, e.g., solder.
When an AC voltage or a DC voltage superimposed with an AC voltage is applied to the monolithic capacitor, vibration is generated with mechanical distortion due to the piezoelectric or electrostrictive effect. In particular, when a ceramic having a high dielectric constant, such as barium titanate, is used as a dielectric of the monolithic capacitor, the vibration caused by mechanical distortion of the monolithic capacitor is increased. When the vibration is generated in the monolithic capacitor, the generated vibration is transmitted to the circuit board, thus causing the circuit board to vibrate. The vibration of the circuit board may cause vibration noise that is perceptible by the human ear.
To solve the above-mentioned problem, Japanese Unexamined Patent Application Publication No. 8-55752, for example, discloses the following technique. A monolithic capacitor is mounted to a substrate in such a state that surfaces of inner electrodes are oriented perpendicularly to the surface of the substrate. With such an arrangement, even when dielectric ceramics vibrate upon application of a voltage while repeating expansion and restoration in the direction of thickness thereof (i.e., the direction in which the inner electrodes are stacked), the vibration is not directly transmitted to the substrate, whereby vibration noise can be reduced.
However, the monolithic capacitor vibrates not only in the direction of thickness thereof, but also in the planar direction of each inner electrode. Therefore, even when the arrangement disclosed in Japanese Unexamined Patent Application Publication No. 8-55752 is employed, the vibration is not reduced depending on the types of circuit boards.